The present invention relates to an exhaust gas purification system that purifies particulate matters (PM) from the exhaust gas discharged by diesel and other internal combustion engines using a continuous regeneration-type diesel particulate filter (DPF) device and also to a control method thereof.
In the same way as for NOx, CO, and also HC etc., restrictions on the volume of particulate matters (hereinafter “PM”) discharged from diesel internal combustion engines grow severe every year. Techniques for collecting this PM in a filter known as a diesel particulate filter (hereinafter “DPF”) and for reducing the quantity thereof by discharging externally have been developed. DPF devices and continuous regeneration DPF devices supporting a catalyst represent such.
However, even in continuous regeneration DPF devices, increasing exhaust gas pressure as a result of filter clogging has become a problem. Although the PM collected by these continuous regeneration DPF devices is continuously burned and purified, and the DPF will self-regenerate while the exhaust gas temperature is approximately 350° C. or higher, when the exhaust gas temperature is low or the operating condition of an internal combustion engine has a low NO discharge—for example, when an internal combustion engine has a continuously low exhaust gas temperature accompanied by idling or low load/low speed traveling, etc.—the temperature of the exhaust gas drops and the catalyst becomes inactive as a result of the low temperature thereof. Accordingly, as the oxidization reaction does not progress and NO becomes insufficient, the PM is not oxidized, and the filter does not regenerate. Accordingly, the accumulation of PM in the filter continues and clogging thereof is accelerated.
As a measure against this filter clogging, it has been conceived to forcibly burn and remove the collected PM by forcibly raising the exhaust gas temperature, when the amount of clogging has exceeded a predetermined amount. As for means for detecting the filter clogging, there are some methods such as a method for detecting by the differential pressure across the filter, and a method for detecting through determination of the PM accumulation quantity by calculating the quantity of PM collected from the engine operation state from a predetermined map data. Besides, as a means for exhaust gas temperature raising, as disclosed in Japanese patent application Kokai publication No. 2003-239789, for example, there is a method by a fuel injection control of an intra-cylinder injection of so-called multi injection (multi retarded injection) or post injection (posterior injection) etc., or a method by a fuel injection control in a direct fuel injection in the exhaust pipe. In the intra-cylinder injection control, after a main injection at a timing delayed from a normal burn so as to continue the burn at the delayed timing, an auxiliary injection is executed.
With the intra-cylinder injection control, in the case where the exhaust gas temperature is lower than the active temperature of an oxidation catalyst disposed upstream of the filter or supported on the filter, the exhaust gas temperature is raised by executing the exhaust raising control of the multi injection and the exhaust throttle etc. When attaining to the exhaust gas temperature higher than the active temperature by executing the unburned fuel adding control of a post injection and the like, the fuel in the exhaust gas is burned through oxidation catalyst. Thereby the filter is regenerated through burning and removing collected PM after raising the exhaust gas temperature higher than the temperature the PM in the filter can be burned.
Normally with continuous regeneration DPF devices, when the collecting quantity of PM reaches a preset limit, the operating condition of the internal combustion engine is automatically changed to regeneration mode. In this forced regeneration mode operation, the exhaust gas temperature is forcibly raised and the quantity of NOx is increased. And thereby, the collected PM is oxidized and removed from the filter to regenerate the filter.
Moreover, for example, Japanese patent application Kokai publication No. 2004-19496 discloses an exhaust-gas purification system of an internal combustion engine, in which it is possible to restrain deterioration of fuel efficiency by relatively easy controls and to perform the regeneration safely and efficiently. In the exhaust gas purification system, for a first threshold value and a second threshold value are provided for a collected PM quantity, the DPF is heated and regenerated only when the operation condition is at high temperature raising efficiency in the case where the collected PM quantity is not less than the first threshold value but less than the second threshold value, and regeneration is performed in the case where the collected PM quantity becomes the second threshold value or more, even if the operation condition is not at a high temperature raising efficiency.
Then, to solve the problem of oil dilution due to forced regeneration, a method is proposed which not only automatically performs forced regeneration during traveling but also performs a forced regeneration in a vehicle stationary idling condition when a clogged filter is notified to a driver by a DPF lamp and the driver stops the vehicle and presses a manual regeneration switch. In the case of the manual forced regeneration in the vehicle stationary idling condition, a method is also considered which accelerates self-regeneration by performing the exhaust gas temperature raising control and at the same time, closes an exhaust throttle butterfly.
However, in the case of the forced regeneration of a DPF device, exhaust gas temperature is raised through the exhaust gas temperature raising control or the unburned fuel addition control. However, the temperature of engine cooling water is also raised. Therefore, a problem occurs that a driver can misunderstand that the engine overheats and an engine trouble occurs, upon watching the water temperature rise in the water temperature meter in the driver seat.
For example, in the case of manual regeneration, a driver receiving a warning stops the vehicle and presses a manual regeneration switch to perform a forced regeneration. Then, the idle rotating speed is increased at the time of a vehicle stationary idling, a multi injection is performed by closing an exhaust brake, and a post injection is performed when an exhaust gas temperature rises up to an oxidation catalyst activation temperature or higher. However, when performing the multi injection or post injection, the exhaust gas temperature rises and the engine cooling water temperature also rises. Therefore, the water temperature meter in the driver seat also rises due to the cooling water temperature rise, and thereby, upon watching the water temperature meter, the driver may take it that a vehicle trouble such as an engine trouble occurs.
In the case of manual regeneration, because a driver presses a manual regeneration switch to perform regeneration, the driver does not think that an engine trouble occurs even if a water temperature mater rises by previously providing the information showing that a cooling water temperature rises. However, in the case of an automatic traveling regeneration in which the forced regeneration is performed when a vehicle travels, a driver does not know whether a forced regeneration is carried. Therefore, the driver confusedly thinks that an engine trouble occurs when the water temperature meter rises. Therefore, it is necessary to avoid a rise of the water temperature meter during a forced regeneration control.